1. Field of the Invention
The present invention relates to a zoom lens and an information device.
The zoom lens of the present invention can be used as a zoom lens in an imaging device such as a digital camera, film camera, video camera or digital video camera. The information device of the present invention can be used as a digital camera, personal digital assistant or the like.
2. Description of the Related Art
In recent years, a high-performance and compact digital camera has been in demand.
A further increased auto-focusing (hereinafter, referred to as AF) speed has also been in demand in recent years in which the AF is the most common focusing.
In order to downsize the zoom lens, it is necessary to reduce the entire length (the distance from the most object side lens surface to the image plane) of the lenses when used.
Inner focusing or rear focusing which moves a compact and lightweight lens group has been the mainstream AF of the zoom lens in recent years, which enables an AF speed to be increased. However, it is necessary to downsize the focus lens in order to further increase an AF speed.
Considering the application to a high-end digital camera, it is necessary to have a resolution corresponding to an imaging element having at least ten million pixels over the entire zoom area.
As will become apparent below, the zoom lens of the present invention has five lens groups of positive, negative, negative, positive and positive, and is configured to perform focusing by displacing the third lens group. Patent Document 1 (Japanese Patent Publication No. 3716418) and Patent Document 2 (Japanese Patent Publication No. 4401451) disclose a zoom lens which performs focusing by displacing the third lens group of an inner lens group.
Patent Document 1 discloses a specific embodiment in which a zoom lens having five lens groups of positive, negative, negative, positive and positive performs focusing by displacing the third lens group as a focusing group.
However, in the zoom lens disclosed in Patent Document 1, the third lens group of the focusing lens is a large and heavy cemented lens of negative and positive lenses. For this reason, a load for moving the third lens group is increased, and a large driving force is required for achieving high-speed focusing; thus, a driving motor or the like may be increased in size.
The zoom lens of Embodiment 4 in Patent Document 2 includes five lens groups of positive, negative, negative, positive and positive, and is configured to perform the focusing with the third lens group as the focusing group. However, the third lens group of the focusing lens includes a large and heavy configuration having three lenses of negative, positive and negative. For this reason, a load for moving the focusing group is increased, and a large driving force is required for achieving high-speed focusing; thus, a driving motor or the like may be increased in size.